Device, method and system for estimating the termination to a wired transmission-line based on determination of characteristic impedance

ABSTRACT

A system and method for measuring a characteristic impedance of a transmission-line comprises transmitting energy to the line, and shortly after measuring the voltage/current involved and thus measuring the equivalent impedance. The measured characteristic impedance may then be used in order to determine the termination value required to minimize reflections. In another embodiment, the proper termination is set or measured by adjusting the termination value to achieve maximum power dissipation in the terminating device. The equivalent characteristic impedance measurement may be used to count the number of metallic conductors connected to a single connection point. This abstract is not intended to limit or construe the scope of the claims.

FIELD OF THE INVENTION

The present invention relates to the field of measuringtransmission-line parameters, and specifically the characteristicimpedance of a transmission line.

BACKGROUND OF THE INVENTION

Wired communication network topologies may generally be segmented intotwo types: Point-to-point and multi-point (also known as‘point-to-multipoint’, ‘bus’ and ‘shared medium’) networks. Inpoint-to-point topology, the network employs one or more communicationlinks, each link is based on a cable or wires as the communicationmedium and connects exactly two nodes, wherein each node is connected toan end of the cable. In multipoint configuration, multiple nodes areconnected in parallel to the same wired medium is various points alongthe cable. Non limiting examples of point-to-point based communicationnetworks are Local Area Network (LAN) Ethernet IEEE802.3 10BaseT,100BaseTX, EIA/TIA-422 (a.k.a. RS422), ISDN (U-Interface), EIA/TIA-449,IEEE1284, IEEE1394 and USB, and Wide Area Networks (WAN) such as HDSL(High speed Digital Subscriber Line), ADSL (Asymmetric DigitalSubscriber Line) and other xDSL technologies (e.g. SHDSL, SDSL, VDSL,IDSL). Non-limiting examples of LANs employing multipoint topology areEthernet IEEE802.3 10Base2, 10Base5, CAN, LON, and EIA/TIA485 (a.k.a.RS-485). Other multipoint in-home networks include telephone line basedcommunication such as HomePNA™ (Home Phoneline Networking Alliance),described in www.homepna.org, and powerline based communication such asHomePlug™, described in www.homeplug.org.

A non-limiting example of a unidirectional point-to-point communicationlink is shown as network 5 in FIG. 1. The network comprises acommunication link based on two conductors 11 a and 11 b cable. Atransmitter 14 a is connected to one end of the cable at points 7 a and7 b. Respective points 6 a and 6 b at the other end of the cable areconnected to a receiver 13 a and termination 12 a. The signal is coupledto the cable by the transmitter 14 a. The signal energy is propagatedover the cable and absorbed by the termination 12 a, and received by thereceiver 13 a.

The term ‘transmitter’ herein includes any device which is capable ofoutputting energy or driving (or exciting) a signal, including anelectrical signal, in a transmission-line. Such devices includeline-drivers, modems and transceivers, as well as any other devicehaving excitation capability. Such a signal may either be voltage based,current based or a combination of both. Similarly, the term ‘receiver’herein includes any device which is able to receive energy/signal (orany function thereof) from a coupled transmission line and convert it toan electrical form, including line receivers, modems and transceivers.Receivers are assumed herein not to include any terminationfunctionality (such as very high input impedance).

A transmission-line is defined as a medium used to carry a signal from apoint A to a point B. The terms ‘line’, ‘transmission line’, ‘cable’,‘wiring’, ‘wire pair’ as used herein should be interpreted to includeany type of transmission-line, and specifically a metallic transmissionline comprising two or more conductors used to carry electrical signals.Non-limiting examples are coaxial cable, PCB connections and twistedpair, the latter including both UTP (unshielded twisted-pair) and STP(shielded twisted-pair), as well as connections within ApplicationSpecific Integrated Circuits (ASICs). Characteristics of wiredtransmission-lines and their effect over digital data transmission aredescribed for example in National Semiconductor Corporation ApplicationNote 806 (April 1992) entitled: “Data Transmission Lines and theirCharacteristics”, and in National Semiconductor Corporation ApplicationNote 808 (March 1992) entitled: “Long Transmission Lines and Data SignalQuality”. Characteristic impedance is a primary property of a metallictransmission line, and commonly relates to the instantaneous voltagesand currents of waves traveling along the line.

The basic function of the termination 12 a is to fully absorb thesignal/energy propagating in the transmission line. Improper terminationsuch as impedance mismatch will cause reflections (a.k.a ringing,overshoot, undershoot, distortion and resonance) back from thereceiver-connected end to the transmitter-connected end. Suchreflections will commonly degrade the communication characteristics ofthe communication link. Proper line termination becomes increasinglyimportant as designs migrate towards higher data signal transfer ratesover relatively longer lengths or transmission medium. For example, thismay be applied to differential data transmission over two conductorssuch as twisted pair cable. In general, transmission-lines such ascables are treated as transmission-lines when the component wavelengthsof the propagating signal, such as an electrical signal in a cable, isshorter than the physical length of the transmission-line. Theimportance of a proper line termination is discussed for example inNational Semiconductor Corporation Application Note 108 (July 1986)entitled: “Transmission Line Characteristics”. A proper line terminationtypically enables better ability to reliably recover a transmittedsignal by using simpler means, as well as improving noisesusceptibility.

Analysis of reflections can be found in the National SemiconductorCorporation Application Note 807, (March 1992) entitled: “Reflections:Computations and Waveforms”, and the manner in which reflections impacton data transmission systems is described in the National SemiconductorCorporation Application Note 903 (August 1993) entitled: “A Comparisonof Differential Termination Techniques”.

Generally, in order to avoid reflection, the termination impedanceshould match the characteristic impedance of the transmission line inthe frequency band of the discussed signal. If the cable parameters areknown, and in particular its characteristic impedance (commonlydesignated as Z0), a good practice is to install a termination (a.k.a.terminator) 12 a of the same value (Z0). In many cases, the cableparameters may be unknown. For example, the cable may exist in a walland/or be of unknown type. Furthermore, cables may be manufactured withrelatively large parameters tolerances, resulting in variations ofcharacteristic impedance from batch to batch. Similarly, thecharacteristic impedance may change due to environmental conditions suchas temperature, humidity and also over time. In any case wherein thecable parameters are not known, a measurement needs to be performed inorder to establish the cable characteristic impedance, and accordinglyterminating the line. Such measurement requires expertise, is laborextensive and time consuming.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method and system for allowing easy and simplemeasuring of characteristic impedance, upon which a proper terminationof a transmission line may be calculated, for example. Such system maybe applied to transmission lines in general, and wired networks inparticular, and specifically for a metallic transmission line having anunknown or changing characteristic impedance.

A multi-point based network (a.k.a. bus or multidrop network) is shownas network 10 in Figure la. Two conductors 11 a and 11 b are used as thecommunication medium, wherein multiple nodes are connected thereto, eachnode connected at a distinct point along the line. The network is shownin a state wherein node 14 a connected to the two conductors 11 a and 11b of the line at respective connection points 18 a and 18 b is atransmitter, while all other nodes serve as receivers. Nodes 13 a, 13 band 13 c serve as receivers and are connected to the line at respectivepoints (17 a, 17 b), (18 a, 19 b) and (8 a, 9 b) respectively. Similarto the above discussion, a termination (equal to the line characteristicimpedance) is connected to each end, wherein terminations 12 a and 12 bare respectively connected to the transmission line ends (15 a, 15 b)and (16 a, 16 b).

Typically in wired communication, the wiring characteristic impedance isnear pure resistance (non-complex impedance); hence each terminationcould be a simple resistor having a resistance equal to thecharacteristic impedance. Such resistors 23 are shown as terminationsand are connected to the transmission line end points (such as 16 a, 16b) of network 20 shown in FIG. 2.

While the metallic transmission line 5 shown in FIG. 1 is a non-tapped,single-path, homogenous and continuous wiring, a transmission line maysometimes involves a tap (a.k.a stub, bridge, and bridge-tap) or anyother discontinuity. Such medium is shown in FIG. 2 as network 20. Inaddition to the two conductors 11 a and 11 b, the network employs anadditional wiring part (a tap) comprising two conductors 21 a and 21 b,tapped in connection points 22 a and 22 b respectively. Similar to theabove discussion, a termination is required in each line end, hencerequiring resistor 23 c connected across the tap end points 24 a and 24b. Similarly, a wired network may employ multiple such taps. Hence for aline having arbitrary topology such as ‘star’, ‘tree’ or any combinationthereof, the taps may be without any node connection (such as shown innetwork 20), or may have nodes connected thereto. In addition, nodes maybe connected to one or more of the line ends, in parallel to thetermination.

In a multi-point environment, while termination is essential in allwiring ends in order to reduce reflections, it is equally important notto introduce termination at all points other than the cable ends. Anyimpedance connected will cause a mismatch and a signal propagated willintroduce reflections at that point. As such, the nodes 13 a, 13 b and13 c should exhibit high impedance in their connection points to thetransmission line.

In many cases, nodes (in particular receivers) comprise a built-intermination/resistor. If the node is connected in one of the line ends,the termination should be connected in parallel to the node. However, ina configuration wherein the node is not located in the line ends, thetermination should be disconnected or disabled, in order to avoidgeneration of reflections. Such distinction between the connectionlocations complicates the network installation. Furthermore, in somecases the wiring topology is not easily known, such as in the case ofin-wall existing wiring. Identifying the topology in order todistinguish between line ends and other points may be complex, laborintensive and expensive.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method and system for allowing easy and simpletermination of a transmission line in general, and wired networks inparticular, and specifically for a metallic transmission line havingmultiple connection points, unknown to be either ends or in the middleof a wiring system.

Wired Home Networking.

Most existing offices and some of the newly built buildings facilitate adata network structure based on dedicated wiring. However, implementingsuch a network in existing buildings typically requires installation ofnew wiring infrastructure. Such installation of new wiring may beimpractical, expensive and problematic. As a result, many technologies(referred to as “no new wires” technologies) have been proposed in orderto facilitate a LAN in a building without adding new wiring. Some ofthese techniques use existing utility wiring installed primarily forother purposes such as telephone, electricity, cable television (CATV),and so forth. Such an approach offers the advantage of being able toinstall such systems and networks without the additional and oftensubstantial cost of installing separate wiring within the building.

The technical aspect for allowing the wiring to carry both the service(such as telephony, electricity and CATV) and the data communicationsignal commonly involves using FDM technique (Frequency DivisionMultiplexing). In such configuration, the service signal and the datacommunication signals are carried across the respective utility wiringeach using a distinct frequency spectrum band. The concept of FDM isknown in the art, and provides means of splitting the bandwidth carriedby a medium such as wiring. In the case of telephone wiring carryingboth telephony and data communication signals, the frequency spectrum issplit into a low-frequency band capable of carrying an analog telephonysignal and a high-frequency band capable of carrying data communicationor other signals.

A network in a house based on using powerline-based home network is alsoknown in the art. The medium for networking is the in-house power lines,which is used for carrying both the mains power and the datacommunication signals. A PLC (Power Line Carrier) modem converts a datacommunication signal (such as Ethernet IEEE802.3) to a signal which canbe carried over the power lines, without affecting and being affected bythe power signal available over those wires. A consortium named HomePlugPowerline Alliance, Inc. of San Ramon, Calif. USA is active instandardizing powerline technologies. A powerline communication systemis described in U.S. Pat. No. 6,243,571 to Bullock et al., which alsoprovides a comprehensive list of prior art publications referring topowerline technology and application. An example of such PLC modemhoused as a snap-on module is HomePlugl.0 based Ethemet-to-PowerlineBridge model DHP-100 from D-Link® Systems, Inc. of Irvine, Calif., USA.Outlets with built in PLC modems for use with combined data and powerusing powerlines are described in US Patent Application 2003/0062990 toSchaeffer et al entitled ‘Powerline bridge apparatus’. Such poweroutlets are available as part of PlugLAN™ by Asoka USA Corporation ofSan Carlos, Calif. USA.

Similarly, carrying data over existing in home CATV coaxial cabling isalso known in the art, for example in US Patent application 2002/0166124to Gurantz et al. An example of home networking over CATV coaxial cablesusing outlets is described in US Patent application 2002/0194383 toCohen et al. Such outlets are available as part of HomeRAN™ system fromTMT Ltd. of Jerusalem, Israel.

Telephony Definitions and Background

The term “telephony” herein denotes in general any kind of telephoneservice, including analog and digital service, such as IntegratedServices Digital Network (ISDN).

Analog telephony, popularly known as “Plain Old Telephone Service”(“POTS”) has been in existence for over 100 years, and is well designedand well engineered for the transmission and switching of voice signalsin the 300-3400 Hz portion (or “voice band” or “telephone band”) of theaudio spectrum. The familiar POTS network supports real-time,low-latency, high-reliability, moderate-fidelity voice telephony, and iscapable of establishing a session between two end-points, each using ananalog telephone set.

The terms “telephone”, “telephone set”, and “telephone device” hereindenote any apparatus, without limitation, which can connect to a PublicSwitch Telephone Network (“PSTN”), including apparatus for both analogand digital telephony, non-limiting examples of which are analogtelephones, digital telephones, facsimile (“fax”) machines, automatictelephone answering machines, voice (a.k.a. dial-up) modems, and datamodems.

The terms “data unit”, “computer” and “personal computer” (“PC”) areused herein interchangeably to include workstations, Personal DigitalAssistants (PDA) and other data terminal equipment (DTE) with interfacesfor connection to a local area network, as well as any other functionalunit of a data station that serves as a data source or a data sink (orboth).

In-home telephone service usually employs two or four wires, to whichtelephone sets are connected via telephone outlets.

Home Networking Existing in-House Wiring.

Similarly to the powerlines and CATV cabling described above, it isoften desirable to use existing telephone wiring simultaneously for bothtelephony and data networking. In this way, establishing a new localarea network in a home or other building is simplified, because there isno need to install additional wiring. Using FDM technique to carry videoover active residential telephone wiring is disclosed by U.S. Pat. No.5,010,399 to Goodman et al. and U.S. Pat. No. 5,621,455 to Rogers et al.

Existing products for carrying data digitally over residential telephonewiring concurrently with active telephone service by using FDM commonlyuses a technology known as HomePNA (Home Phoneline Networking Alliance)whose phonelines interface has been standardized as ITU-T (ITUTelecommunication Standardization Sector) recommendation G.989.1. TheHomePNA technology is described in U.S. Pat. No. 6,069,899 to Foley,U.S. Pat. No. 5,896,443 to Dichter, U.S. Patent application 2002/0019966to Yagil et al., U.S. Patent Application 2003/0139151 to Lifshitz et al.and others. The available bandwidth over the wiring is split into alow-frequency band capable of carrying an analog telephony signal(POTS), and a high-frequency band is allocated for carrying datacommunication signals. In such FDM based configuration, telephony is notaffected, while a data communication capability is provided overexisting telephone wiring within a home.

Outlets

The term “outlet” herein denotes an electromechanical device, whichfacilitates easy, rapid connection and disconnection of external devicesto and from wiring installed within a building. An outlet commonly has afixed connection to the wiring, and permits the easy connection ofexternal devices as desired, commonly by means of an integrated standardconnector in a faceplate. The outlet is normally mechanically attachedto, or mounted in, a wall or similar surface. Non-limiting examples ofcommon outlets include: telephone outlets for connecting telephones andrelated devices; CATV outlets for connecting television sets, VCR's, andthe like; outlets used as part of LAN wiring (a.k.a. structured wiring)and electrical outlets for connecting power to electrical appliances.The term “wall” herein denotes any interior or exterior surface of abuilding, including, but not limited to, ceilings and floors, inaddition to vertical walls.

Functional Outlet Approach.

This approach involves substituting the existing service outlets with‘network’ active outlets. Outlets in general (to include LAN structuredwiring, electrical power outlets, telephone outlets, and cabletelevision outlets) have evolved as passive devices being part of thewiring system house infrastructure and solely serving the purpose ofproviding access to the in-wall wiring. However, there is a trendtowards embedding active circuitry in the outlet in order to use them aspart of the home/office network, and typically to provide a standarddata communication interface. In most cases, the circuits added servethe purpose of adding data interface connectivity to the outlet, addedto its basic passive connectivity function.

An outlet supporting both telephony and data interfaces for use withtelephone wiring is disclosed in U.S. Pat. No. 6,549,616 entitled‘Telephone outlet for implementing a local area network over telephonelines and a local area network using such outlets’ to Binder. Suchoutlets are available as part of NetHome™ system from SercoNet Ltd. ofRa'ananna, Israel.

Another telephone outlet is described in U.S. Pat. No. 6,216,160 toDichter, entitled ‘Automatically configurable computer network’. Anexample of home networking over CATV coaxial cables using outlets isdescribed in WO 02/065229 published 22 Aug., 2002 entitled: ‘CableranNetworking over Coaxial Cables’ to Cohen et al. Such outlets areavailable as part of HomeRAN™ system from TMT Ltd. of Jerusalem, Israel.Outlets for use in conjunction with wiring carrying telephony, data andentertainment signals are disclosed in US Patent ApplicationUS2003/0099228 to Alcock entitled ‘Local area and multimedia networkusing radio frequency and coaxial cable’. Outlets for use with combineddata and power using powerlines are described in US Patent ApplicationUS2003/0062990 to Schaeffer et al. entitled ‘Powerline bridgeapparatus’. Such power outlets are available as part of PlugLAN™ byAsoka USA Corporation of San Carlos, Calif. USA.

While the active outlets have been described above with regard tonetworks formed over wiring used for basic services (e.g. telephone,CATV and power), it will be appreciated that the invention can beequally applied to outlets used in networks using dedicated wiring. Insuch a case, the outlet circuitry is used to provide additionalinterfaces to an outlet, beyond the basic service of single dataconnectivity interface. For example, it may be used to provide multipledata interfaces wherein the wiring supports single such data connection.An example of such outlet is the Network Jack™ product familymanufactured by 3Com™ of Santa-Clara, Calif., U.S.A. In addition, suchoutlets are described in U.S. Pat. No. 6,108,331 to Thompson entitled‘Single Medium Wiring Scheme for Multiple Signal Distribution inBuilding and Access Port Therefor’ as well as U.S. Patent Application US2003/0112965 Published Jun. 19, 2003 to McNamara et al. entitled ‘ActiveWall Outlet’.

While the active outlets have been described with regard to outlets andnetworks based on conductive media such as wires and cables, it will beappreciated that such outlets are equally applicable in the case whereinthe network medium is non-conductive, such as fiber-optical cabling.Active outlets supporting data interfaces and based on fiber opticcabling are described in U.S. Patent Application US 2002/0146207Published Oct., 10 2002 to Chu, entitled ‘Fiber Converter FaceplateOutlet’, as well as in U.S. Pat. No. 6,108,331 to Thompson entitled‘Single Medium Wiring Scheme for Multiple Signal Distribution inBuilding and Access Port Therefor’. As such, the term ‘wiring’ as usedin this application as well as in the appended claims should beinterpreted to include networks based on non-conductive media such asfiber-optics cabling.

While the outlets described above use active circuitry for splitting thedata and service signals, passive implementations are also available. Anexample of such a passive outlet is disclosed in WO 02/25920 to Binderentitled ‘Telephone communication system and method over local areanetwork wiring’. Such outlets are available as part of the etherSPLITsystem from QLynk Communication Inc. of College Station, Tex. USA.etherSPLIT is a registered trademark of Dynamic Information Systems.

The described above outlets are complete and self-contained devices. Assuch, they can be easily installed in new houses instead of regularpassive simple outlets. However, such solutions are not appropriate inthe case of retrofitting existing wiring systems. In most cases, anysuch modification will require dismantling the existing outlets andinstalling the new ones having the improved features. Such activity iscumbersome, expensive and will often require professional skill.Furthermore, owing to safety aspects involved while handling hazardousvoltages (such as in the powerlines and telephone lines), localregulations may require only certified personnel to handle the wiring,making it expensive and militating against a do-it-yourself approach.

Furthermore, as the technology and environment change in time, a need toupgrade, modify or change the outlet functionalities, features andcharacteristics may arise. For example, the data interface may need tobe upgraded to interconnect with new standards. In another example, thecircuitry may need to be upgraded to support higher bandwidth.Similarly, management and Quality of Service (QoS) functionalities mayneed to be either introduced or upgraded. In yet other examples,additional functionalities and interfaces may need to be added. Usingcomplete self-contained outlets as a substitute to the existing onesalso introduces the disadvantages described above.

Plug-in Device.

One approach to adding functionality to existing outlets is by using aplug-in module. Such plug-in modules are described in US PatentApplication US 2002/0039388 to Smart et al entitled ‘High data-ratepowerline network system and method’, US Patent Application US2002/0060617 to Walbeck et al. entitled ‘Modular power line networkadapter’ and also in US Patent Application US 2003/0062990 to Schaeffer,J R et al. entitled ‘Powerline bridge Apparatus’. Such a module usingHomePlug™ technology are available from multiple sources such as part ofPlugLink™ products by Asoka USA Corporation of San Carlos, Calif., USA.HomePlug is a trademark of HomePlug Powerline Alliance, Inc. of SanRamon, Calif., USA. Various types of snap-on devices are also describedin WO 04/001034.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a transmission linecharacteristic impedance is measured by applying regular lumpedimpedance/resistance measuring. Any other lumped or distributedimpedance/resistance measuring technique known in the art may be equallyapplied. In one aspect of the invention the measurement is based ontransmitting, sourcing or exciting an electrical signal, either voltageor current (or both). In one aspect of the invention the measurement isbased on exciting a known energy into the transmission-line, andmeasuring the current flow to the transmission line directly orindirectly such as using voltage divider. The measured values are usedto calculate the transmission-line characteristic impedance. Measuringthe characteristic impedance may be initiated periodically, uponreceiving an external electrical signal (e.g. from another system), uponmanually applying a signal, or upon powering up, or upon sensing anyother signal excitation such as packet or session as part of a datacommunication session.

In order to allow proper measurement, no other signals (such asreflections or data communication signals) should exist and affect themeasurement. According to one aspect of the invention, the impedance(either lumped or distributed) measuring is executed shortly afterinjecting the measurement signal into the transmission-line, and priorto reflections arrival from taps or non-terminated ends to the measuredtransmission line end. Since practically transmission-lines are nothomogenous and do not have infinite length, reflections from taps,non-homogenous points or non-terminated remote ends occur and willarrive to the measured end. Thus, the measurement should be executed andcompleted shortly after applying the measurement signal, before thereflections arrive to this line end. In order to make any subsequent useof the measured value, the calculated characteristic impedance (or anyfunction thereof such as the voltage/current measured) should be stored.

According to one aspect of the invention the transmission-line serves asa medium for data communication. In such configuration, a modem (beingtransmitter, receiver, transceiver or the like) is connected to a pointalong the transmission-line as well as to the transmission-lineend-point relating to the impedance measurement. Characteristicimpedance measurement may be used to determine whether a termination isrequired in a specific connection point. According to one aspect of theinvention the termination value is determined according to the measuredcharacteristic impedance. For example, the termination value can be setto be equal to the measured lumped impedance in order to minimizereflection in an end-point. In the case wherein data communication isinvolved over the same transmission-line, time domain multiplexing isused to allow both the modem and the measurement to share thetransmission line, wherein the modem operation should be halted duringthe impedance measurement, in order not to interfere with themeasurement and to enable proper and accurate measurement. According toone aspect of the invention, this is achieved by disconnecting the modem(to include transceiver and transmitter) from the transmission-lineduring the measurement phase, and re-connecting it after the measurementis completed. As such, the system may be exclusively in either ameasurement state or a data communication state.

According to one aspect of the invention, a frequency divisionmultiplexing (FDM) approach is applied in order to concurrently carryboth an application signal (such as data communication signal) and animpedance measurement related signal over the transmission-line. In thisarrangement, the measurement system uses a signal carried in one or morefrequency bands distinct from the band wherein the application signal iscarried. The characteristic impedance of the transmission-line in thefrequency band or bands not being part of the measurement system may beapproximated using known extrapolation or interpolation techniques.

According to one aspect of the invention, the measured/calculatedtransmission-line characteristic impedance is used for estimating thecount of wire pairs connected to a single connection point, for use withone or more similar wire pairs having similar nominal characteristicimpedance Z0 and all connected to the single connection point. Byinstantaneously measuring the connection point lumped impedance Z, theconnected wire pairs count can be estimated to be Z0/Z. The estimatedpairs count may be visually indicated to a user as part of a pairs counttest-set.

According to one aspect of the invention, the pair count is used toidentify the end point of an unknown wiring structure. In the casewherein Z=Z0, a single wire pair connection-point is detected, thusrequiring a termination to be connected to this point in order tominimize reflections from this wire-pair end-point.

According to one aspect of the invention in-wall hidden wire-pairs aremeasured. Such wire pairs may comprise telephone, AC power or CATVwiring infrastructure, as well as any other wiring. The wire pair may becarrying service signals (such as telephone, AC power or CATV signals),and may be accessed via outlets (such as telephone, AC power or CATVoutlets). In the case wherein outlets are used to connect to the wiring,the impedance measuring or the termination setting or both circuits maybe integrated (in part or in full) into the outlet.

According to one aspect of the invention for use with atransmission-line carrying a signal and having a nominal characteristicimpedance and terminated with a impedance-controlled termination, theproper termination value (having the same value as the nominalcharacteristic impedance) is matched to the transmission-line by using aclosed control loop, wherein the power dissipated by theimpedance-controlled termination (connected to the transmission-line) ismeasured and used for changing the impedance-controlled terminationvalue to obtain a maximum power dissipation. The power dissipation bythe termination can be measured directly by sensing the voltage acrossor the current flowing through the termination. Alternatively, thedissipated power is indirectly measured by measuring a physicalphenomena affected by the dissipated power (e.g. heat).

The measuring system (in whole or in part) may be enclosed as astand-alone unit, housed/integrated as part of a modem, or housed inintegrated form as part of a service outlet or as a snap-on module.Similarly, the termination setting system (in whole or in part) may bestand-alone, or housed/integrated as part of a modem, or housed inintegrated form as part of a service outlet, or as a snap-on module

The above summary is not an exhaustive list of all aspects of thepresent invention. Indeed, the inventor contemplates that his inventionincludes all systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the detailed description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

It is understood that other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein are shown and described only embodimentsof the invention by way of illustration. As will be realized, theinvention is capable of other and different embodiments and its severaldetails are capable of modification in various other respects, allwithout departing from the scope of the present invention as defined bythe claims. Accordingly, the drawings and detailed description are to beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of non-limiting example only,with reference to the accompanying drawings, wherein like designationsdenote like elements.

FIG. 1 illustrates schematically a point-to-point network.

FIG. 1 a illustrates schematically a multi-point network.

FIG. 2 illustrates schematically a multi-point network with a tap.

FIG. 3 illustrates schematically a general functional block diagram ofan exemplary Characteristic Impedance Meter (CIM) according to theinvention.

FIG. 4 illustrates schematically a general functional block diagram ofan exemplary termination system according to the invention.

FIG. 5 illustrates schematically a general functional block diagram ofan exemplary Characteristic Impedance Meter (CIM) according to theinvention.

FIG. 6 illustrates schematically a general functional block diagram ofan exemplary Voltage controlled Resistor (VCR).

FIG. 7 illustrates schematically a general functional flow chart of anexemplary operation according to the invention.

FIG. 8 a illustrates schematically a general termination system.

FIG. 8 b illustrates schematically a general functional block diagram ofan exemplary termination system according to the invention.

FIG. 9 illustrates schematically a general functional block diagram ofan exemplary pairs counting system according to the invention.

FIG. 10 illustrates schematically a frequency bands allocation schemeaccording to the invention.

FIG. 11 illustrates schematically a general functional block diagram ofan exemplary termination system according to the invention.

FIG. 12 illustrates schematically a graph of a dissipated power versus atermination resistance.

FIG. 13 illustrates schematically a telephone-wiring infrastructure in ahouse.

FIG. 14 illustrates schematically an AC-power wiring infrastructure in ahouse.

FIG. 15 illustrates schematically an exemplary termination test-setaccording to the invention.

FIG. 16 illustrates schematically an exemplary AC power wiringtermination device according to the invention.

FIG. 17 illustrates schematically a typical packet structure.

FIG. 18 illustrates schematically a general functional block diagram ofan exemplary termination system according to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The principles and operation of a network according to the presentinvention may be understood with reference to the drawings and theaccompanying description wherein similar components appearing indifferent figures are denoted by identical reference numerals. Thedrawings and descriptions are conceptual only. In actual practice, asingle component can implement one or more functions; alternatively,each function can be implemented by a plurality of components andcircuits. In the drawings and descriptions, identical reference numeralsindicate those components that are common to different embodiments orconfigurations.

A part of one embodiment according to the present invention is shown asCharacteristic Impedance Meter (CIM) 30 in FIG. 3. The CIM measures thecharacteristic impedance of a transmission line by applying a signal tothe line, and directly measuring the input impedance into thetransmission line by means of voltage division shortly afterwards. TheCIM 30 measures the characteristic impedance of the Transmission lineUnder Test (T.U.T or TUT) 42 connected via port 39, and having anunknown characteristic impedance Z0. The measurement sequence startsupon sensing a MEASURE signal in port 31, signaling the CIM to start themeasurement process. The MEASURE signal at port 31 is fed to pulsegenerator 32, which outputs a pulse shown as square wave pulse signal33. The pulse signal waveform 33 starts at time T0, is τ seconds longand has an amplitude of V′ volts. In the case wherein the characteristicimpedance is required to be measured in a specific and/or limitedfrequency band, the pulse signal is then fed to a band-pass filter 34limiting the signal energy to the required band. If the signal isgenerated having the frequency spectrum required, and/or if no frequencyband limitations exists, such a filter 34 may be omitted. After beingfiltered by the filter 34, the pulse is connected to the TUT 42 via theseries resistor Rs 36 connected to the port 39. The processing unit 37is considered to have very high input impedance, hence does notinterfere with the signal. The voltage at port 39 (and at the input tothe processing unit 37) is as such a voltage formed by dividing V′between the resistor Rs and Z0 (pure resistive characteristic impedanceis assumed). As such, the divided voltage Vd at port 39 is:Vd=V′*Z0/(Rs+Z0), assuming no attenuation by the filter 34. In the caseof amplitude attenuation by the filter 34, the voltage V′ reflects theamplitude at the filter 34 output. Since V′ and Rs are known, thevoltage Vd at port 39 is a direct function of the value of thecharacteristic impedance Z0. In order to allow for accurate measurement,the value of resistor Rs should be as close as possible, or at least ofthe same order of magnitude, as the measured impedance Z0. The voltageVd is fed to the processing unit 37, which provides a signal outputwhich is a function of the voltage at port 39. For example, theprocessing unit 37 may provide a voltage proportional to the Vd above.In another example, the processing unit 37 calculates Z0 by the equationZ0=Rs*Vd/(V′−Vd), and provides a signal (e.g. voltage) proportional tothe Z0 calculated. Other transfer functions may also be considered. Ifprocessing is not required, processing unit 37 may be omitted. Assuminga practical and finite length TUT, the pulse signal starts to propagatealong the transmission line, and assuming taps, non-terminated ends orany other non-continuities, a reflection signal will appear at port 39,causing the measured Vd to be inaccurate and not to reflect the actualvoltage division discussed. As such, an accurate value of Vd exists atport 39 only for a short period after the pulse signal start (T0).Hence, there is a need to latch and store the value at this instant.

The pulse signal 33 is also provided to a delay unit 35. After apredetermined delay period (after T0), a signal is output to the triggerinput of a sample and hold unit 38, which latches and holds the signaloutput from processing unit 37 as signal Vm at port 41. Hence, signal Vm(e.g. voltage) represents a function of the TUT characteristic impedanceZ0. The delay value should not be too short, in order to allow anaccurate and fully stabilized value. On the other hand, the delay valueshould not be too long in order to obviate the effect of reflections.The value of τ should be small enough in order not to occupy thetransmission line for long and to minimize the period required for themeasurement. Similarly, the value of τ should be long enough to allowaccurate and stabilize measurement. In a system that has been built andtested, a pulse of τ=15 nanoseconds enabled accurate reflection-freemeasurement of any twisted-pair cable longer than 70 centimeters.

Hence, a known while after a MEASURE signal is sensed in port 31, theCIM will output in port 41 a signal which represents the value of thecharacteristic impedance Z0 of the TUT 42 connected in port 39.

The CIM 30 above is operative to measure the characteristic impedance ofthe TUT 42. After such measurement is performed, adequate terminationshould be provided based on the measured value. A system 40 providingboth measurement and setting of the required termination value is shownin FIG. 4. The TUT 42 shown in the figure is connected via a switch 44,having two distinct states, designated as M (Measurement) and S(Setting), the states being selected by a control signal line SELECT 49.In measurement (M) state, the TUT 42 is connected to the CIM 30 port 39,as described in FIG. 3 above. In such a state, upon application of aMEASURE signal to port 31 of the CIM 30, the CIM 30 will perform themeasurement function, resulting in a continuous Vm signal representingthe measured characteristic impedance Z0 value. The Vm signal at port 41of the CIM 30 drives the Termination Setting (TS) unit 43. The TS 43functions to exhibit the required termination value. Typically, animpedance value equal to the measured characteristic impedance Z0 willbe used for termination, in order to minimize mismatch and reflections.At the end of the measurement period, line SELECT control 49 of switch44 shifts to S (Setting) mode. The TUT 42 is thus disconnected from theCIM 30 and connects to the TS via line 45, resulting in a correcttermination value at the end of the TUT 42, whereby the TUT is operativeto be used as a communication medium terminated by unit 43.

As described above, the characteristic impedance is measured usinglumped impedance measuring technique, thus treating thetransmission-line as lumped entity rather than a distributed one. Suchapproach is valid under one or more of the following assumptions:

a. No energy (other than the signal used for impedance measuring) isbeing transmitted over the transmission line and received by themeasuring device during the measurement cycle. As such, the measurementis solely based on the energy transmitted to the transmission-line bythe measuring device, having a known value. Other energy received mayimpact on the accuracy of the impedance measurement.

b. Infinite length transmission line. In a very long and homogenoustransmission line (e.g. having no taps/bridges and no impedance changesalong the line) no reflections are generated, thus no signal interfereswith the impedance measurement.

c. The measurement is executed before reflections are received in theconnected end. In this scenario, it is assumed that at least a shortlength of the transmission line at the end used for the measurement ishomogenous (e.g. no taps or impedance change), hence causing noreflections. The time interval until any reflections or any otherinterfering signals reach the end used for measurement is used forcompleting the impedance measurement, thus gaining accurateno-reflection affected measuring cycle. For example, assuming thenearest interfering point (e.g. line end point or tap) is at a pointhaving a distance X from the measuring end, and assuming the signalpropagation speed over the transmission line is V (usually close to thespeed of light), this point will generate a reflection signal (as aresult of the transmitted measurement signal) that will reach thetransmission line end after a time delay of 2*X/V. During this time, anaccurate interference-free measurement may be executed.

Under the above conditions a lumped impedance measurement will providethe transmission-line characteristic impedance. Any lumped impedance orresistance measurement mechanism may be used. In most cases, Ohm's lawis used as the basis of such measurement. One example is shown in theCIM 30, wherein voltage excitation is applied to the TUT, and thecurrent flowing is measured by the voltage created over a voltagedivider resistor network. However, any other lumped impedance orresistance measurement mechanism may be equally used. Such an example isCIM 50 illustrated in FIG. 5. CIM 50 is based on CIM 30 structure,however the characteristic impedance lump measurement is based ondirectly measuring the current I flowing through the TUT 42 by anammeter (a.k.a. amperemeter) 82 and the voltage V across the TUT by avoltmeter 85. The processing unit 37 calculates the characteristicimpedance by using Ohm's law R=V/I. In both cases of CIM 30 and CIM 50,either current or voltage excitation may be used, as well as acombination of both current and voltage excitation.

While the invention has been demonstrated with a few Ohm's lawimpedance/resistance measurement examples, it will be appreciated thatthe invention can equally be applied to any other impedance orresistance lumped measurement. Furthermore, any non-lumped measurementbased on lumped or non-lumped transmission-line electrical parametersmay equally be used. Furthermore, the impedance may be measured based onany transmission-line physical parameters other than electricalparameters.

In one embodiment according to the present invention the TerminationSetting (TS) 43 is based on a Voltage Controlled Resistor (VCR). Animplementation of such VCR is known in the art, and a non-limitingexample will be based on Xicor X9015 Single Digitally ControlledPotentiometer (XDCP™), available from Intersil Corporations of Milpitas,California U.S.A.

The Termination Setting (TS) described above has a continuous settingrange for the termination value. Similarly, the TS may be operative toselect from a fixed set of predetermined values. Such a TerminationSetting (TS) 60 is shown in FIG. 6, having two discrete values, infinityand Rts. A comparator 51 compares the incoming voltage Vm to apredetermined value. In the case wherein the Vm is above the setthreshold, a signal is sent to the Switch Driver 52, which in turnoperates, via a control line 55, a switch 54, which in turn connects theresistor Rts 53 to the TUT via port 45. In the case wherein the value ofVm does not cross the threshold, the switch 54 remains in the openstate, resulting in a non-connected termination to the line 45,effectively an infinite resistance value. Similarly, multiplenon-infinite values can be switched in as a function of the Vm inputvalue. Switch 54 may be implemented by relay contacts, wherein line 55is the coil operating signal or may be implemented using solid statecircuitry as known in the art.

TS 60 may be used in order to decide whether a termination should beinserted or not. In the case of wiring having multiple connection pointsand unknown topology, there is a need to identify the wiring ends inorder to connect a termination thereto, and to identify points that arenot ends (referred to as non end connection points) and must be leftopen. An example may be the wiring 11 of system 20, having end points15, 16 and 24, as well as non end connection points 17, 18, 19 and 9 (itis assumed that terminations 23 a, 23 b and 23 c are not connected).Applying CIM 30 at an end point (such as 15, 16 and 24) will result in aVm value representing the wiring 11 characteristic impedance value.Similarly, applying the CIM 30 to a non end connection point, willresult in a Vm value of half of the characteristic impedance value,since each wiring segment connected represents its own characteristicimpedance value, thus resulting in two identical values connected inparallel. In the case of a tap, such as connection point 22 in wiring 11in system 20, wherein three branches are effectively connected, theequivalent value measured by the CIM 30 will be a third of thecharacteristic impedance. Since only the end-points are to be equippedwith a termination, a TS 60 with a comparator 51 having a thresholdequal, for example, to 0.75 of the nominal characteristic value may beused. End-points will be identified as above the threshold level, andhence will result in connection of the characteristic impedance resistorRts 53, while non end-point connections will be automatically left open.

Process Flow.

The operations of the process involving automatic termination system areshown as flow chart 70 in FIG. 7. Starting from the Start operation 71,the TUT is disconnected in operation 72 from the modem, for example, andconnects in operation 73 to a CIM. The CIM transmits energy for a shortwhile into the TUT (in operation 74), and measures a voltage (or anyother parameter) based on the TUT characteristic impedance (operation75). The value measured which represents the TUT characteristic value isstored in operation 76. After the measuring is completed, the TUT isdisconnected from the CIM (operation 77) and reconnected to a normalstate of communication operation. Based on the measured value inoperation 75, the required termination value (e.g. resistor value equalto the characteristic impedance) is calculated (operation 78) andconnected to the TUT. In the example of system 40 above, operations 77,78 and 79 can be carried out with the aid of TS 43 and switch 44.

While the above process may be employed only once in the systemlifetime, such as only as part of the initial installation, in someembodiments the process may be repeated more than once. For example, theprocess may be repeated every time the system is being powered orperiodically. In the latter cases, the process will be re-initiatedafter a delay, as described as operation 69.

As shown in the chart 70, the system may be in one of two states. Thefirst state is the measuring state, comprising operations 72 to 78,during which the TUT parameters are measured, and the regular operationstate (comprising operation 79) in which the proper termination isconnected and the system operates as a wired communication system.During the regular operation state, the system uses a termination basedon the measurement result of the measuring state. As such, a valuerepresenting the characteristic termination (or any function thereof)must be calculated and stored in the measuring state, to be used in theregular operation state. Such storing may use mechanical storage (suchas a multi-state mechanical switch), analog value storing (such as‘sample and hold’ circuitry) or digital memory.

Reflections Computations.

Computations of the voltage and current involving the boundaryconditions of a transmission line are known in the art, as exampled anddetailed in National Semiconductors Application Note 807 (AN-807) datedMarch 1992. Calculations will be presented based on assuming a twoconductor transmission line consisting of conductors 11 a and 11 b,having R0, a pure resistive characteristic impedance, and terminated atone end (points 81 a, 81 b) by a termination resistor 23 d havingresistance R1, as shown in system 80 a shown in FIG. 8 a. A signalhaving a voltage value of Vx and current value of Ix is propagated inthe transmission line (from ‘left’ to ‘right’). By definition, theequation Vx=R0*Ix applies, and the energy propagated is equal toPx=Ix*Vx=VXˆ2/R0, and for simplicity's sake, no energy loss in thetransmission line is assumed. Part of the propagated energy is absorbedin the termination resistor 23 d, resulting in a voltage level of V1 andcurrent of I1, related by V1=I1*R1. In the case of matched termination(R1=R0), all the propagating energy will be absorbed by the terminationresistor 23 d, and no reflections will be generated. In the case whereinthere is no matching termination, a reflection signal having a voltageof Vr and current value of Ir will be propagated from the end point(from ‘right’ to ‘left’), wherein Vr=Ir*R0 applies. Applying Kirchhoff'slaw to the end point (81 a, 81 b), the current equation is I1=Ix−Ir andthe voltage equation is Vl=Vx+Vr. Similarly, applying the principle ofenergy conservation, Px=P1+Pr.

Manipulating the above equations results in thatP1=4*R1*Vxˆ2/[Ro+R1)ˆ2]. This function is shown schematically as graph120 in FIG. 12, wherein the X-axis 123 represents the R1 value and theY-axis 122 represents the resulting P1. The curve 121 represents theabove value of P1 as a function of the parameter R1. Furthercalculations show that this P1 function has a single maximum at R1=R0,shown as line 124 in graph 120, wherein the transmission line is fullymatched, and the whole Px energy is absorbed in the termination (P1=Px),and no reflections are generated (Pr=0).

The above calculations suggest that tuning the termination value R1 toobtain the maximum energy dissipation over this terminating resistor,will effectively result in a well-matched termination. One option is tomanually tune the termination resistance value (while energy is carriedin the transmission line) while measuring the energy absorbed therein,and fixing the steady-state value to the value resulting in the maximumenergy.

Alternatively, the termination value may be automatically tuned to matchthe characteristic impedance by maximizing the power absorption in thetermination. Such a system 80 b is illustrated in FIG. 8 b. A tunabletermination 83, such as a VCR (Voltage Controlled Resistor) is connectedto the end points 81 a, 81 b of a line (11 a, 11 b), being energized bya driver 14 a. The current flowing through the termination 83 ismeasured by a current-meter (ammeter) 82, while the voltage across thetermination 83 terminals is measured by a voltage-meter (voltmeter) 85.The metered current and voltage values are multiplied in the multiplier86, resulting in a signal which represent the power dissipating in thetermination 83 (P=I*R). Similarly, only the current may be measured, andthe power calculated by P=Iˆ2*R, or alternatively only the voltage maybe measured, using the equation P=Vˆ2/R to obtain the power. In yetanother embodiment, the power is measured not directly by measuringvoltage or current, bur rather by the effective power dissipated. Forexample, assuming that the power is converted into heat, temperature maybe measured as an indication of the dissipated power.

The power representing signal is fed from multiplier 86 via line 88 to acontrol unit 87, which in turn controls the termination 83 resistancevalue via line 89. The control unit 87 is operative to effect a closedloop to set the resistance value of the VCR 83 to obtain the maximumpower indication on line 88.

One advantage of system 80 b is that no dedicated power signal isrequired to be transmitted into the transmission line as part of themeasurement process, but the system rather uses existing energy in thetransmission line (for example, as part of normal operation). However,in many cases, proper operation of the system 80 b requires a minimumreceived energy in the termination 83. In one embodiment, a comparator84 senses the voltage level (as an indicator of the received powerlevel), and allows the operation of the connected control unit 87 onlyupon sensing a signal level above a predefined level, ensuring properloop operation.

Similar to the above discussion, the control loop in system 80 b may beoperated once (e.g. as part of the initial installation, upon manualintervention or as part of any power-on process), periodically orcontinuously.

System 80 b has been so far described with regard to matching a propertermination value to the end point of a transmission line. In the casewherein the system in connected to a non end point, such as connectionpoints 9, 17 and 18 in system 20 in FIG. 2, part of the ‘hitting’ energyPx continues to propagate along the transmission line. Applying similarcomputations as above results in such a case in an absorbed energy ofP1=2.25*R1*Vxˆ2/[Ro+R1/2)ˆ2]. Further calculations show that this P1function has a single maximum at R1=2*R0. Similarly, N connected lineswill result in maximum absorbed energy when R1=N*R0. Hence, suchmechanism may be used for pairs counting or as an end-point detector asexplained below. Since for best operation of a communication system notermination should be applied to non end-points, any measured valueindicating a tap rather than an end-point (e.g. maximum effected when R1is more than 1.5*R0) should result in disconnection of the terminationused for the measurement purposes.

Pairs Counting.

The characteristic impedance measuring may be used as an indicator foridentifying a topology of hidden wiring. Such application is shown assystem 90 in FIG. 9. A wiring system 92 comprises unknown N-counteddistinct pairs designated 91 a, 91 b up to 91 c, each assumed to havethe same characteristic impedance value Rt, and all being connected to acommon connection point 93. A CIM 30 is connected to the connectionpoint 93, similar to TUT connection. Since the characteristic impedancesof all wirings 91 are connected in parallel, the equivalent impedancemeasured in point 93 is equal to Rt/N. Hence, by measuring thecharacteristic impedance value (represented by voltage Vm), the paircount may be inferred. For example, in the case of five equal cableseach having a characteristic impedance of 100 ohms, the equivalent valuemeasured by the CIM 30 will be 100/5=20 ohms. Such mechanism may also beapplied in order to identify end-points in the case of hidden wiringtopology, since such points reflect the full characteristic value Rt.

Frequency Division Multiplexing (FDM).

System 40 described above is based on transmitting a signal into thetransmission line over the same frequency spectrum used for thecommunication operation. As such, measures need to be taken in order toavoid collisions with the communication signal. Such measures may becomplicated and also limits either the availability to operate themeasurement system or the communication network over the transmissionline. In one or more embodiments, a frequency division/domainmultiplexing (FDM) mechanism is employed, wherein the communicationsignal is carried over a frequency band distinct from that used by thetermination measurement system. An example of a frequency spectrumallocation 100 is shown in FIG. 10, illustrated along frequency axis101. The communication system may use the frequency band 103 allocatedbetween frequencies f1 and f2. The frequency allocation for theautomatic termination system uses the band 102 above frequency f2.

A system 110 utilizing the above FDM concept is shown in FIG. 11. Thecommunication system is based on a modem 113 transmitting/receivingsignals to/from the transmission line 42 through a Band Pass Filter(BPF) 112, passing only signals in the frequency band 103. Thetermination 43 is also connected to the transmission line 42 via the BPF112. The automatic termination system is based on CIM 30, connected tothe transmission line 42 via a Band Pass Filter (BPF) 111, passing onlythe termination system related signals residing in the band 102 (abovefrequency f2). In the frequency allocation 100 shown in FIG. 10, BPF 111may be implemented as a High Pass Filter (HPF) and BPF 112 may beimplemented as a Low Pass filter (LPF).

Working in different and non-overlapping frequency bands, both thecommunication and the automatic termination systems can concurrentlyoperate, both coupled to the same transmission line. Since thetermination value obtained by the automatic termination system(comprising the CIM 30 and the TS 43) relates to a frequency spectrumdistinct from the frequency band used by the communication system, theremay be a need to adjust the measured value in order to adapt from themeasurement band to the communication band. Such adjustments may useknown formulas, a pre-determined scaling or any other adaptation,extrapolation or approximation mechanisms.

While the above description involved the case wherein the automatictermination system used a frequency band above the communication systemfrequency band, other frequency band allocations may be used. Forexample, the termination system may use the frequency band 104 as partof the allocation 100, located below the communication system frequencyband. In such a scenario, the BPF 112 may be implemented by an HPF(passing signals over frequency f1), and the BPF 111 may be implementedby a LPF passing signals under frequency f1.

Furthermore, the measurement system may use bands both below and abovethe communication system band. The measurements in the two bands may beperformed simultaneously (e.g. by two independent CIMs), or be performedusing a single CIM 30 and two distinct filters, each operative at adifferent time. Calculation of the termination value may use bothmeasurements (low and high bands), such as interpolation based on thetwo readings (e.g. averaging).

Investigating Hidden Wirings

One application of the invention involves investigating an unknown andnot-easily accessed wiring infrastructure. An existing telephone wiringin a building is one example. Such existing telephone wiring is hiddenin the walls of a house, and a lot of effort is required to expose thetopology of the wiring. An example of such existing telephone wiringstructure is shown in FIG. 13 as system 130, involving telephone wiringinfrastructure within the walls of a building 132. The in-housetelephone wiring connects to the PSTN (Public Switching TelephoneNetwork) 131 via one or more telephone wire pairs, commonly referred toas the ‘local loop’ or ‘subscriber loop’. The telephone wiring isaccessed in the house via telephone outlets 134 a, 134 b, 134 c and 134d. Each such outlet 134 connects to the in wall wiring, and allows forconnection thereto via a front connector 135 (commonly RJ-11 jack inNorth America), suitable for connection of a telephone set by a suitableplug (RJ-11 plug in North America). As shown for system 130, RJ-11 jacks135 a, 135 b, 135 c and 135 d are respectively part of outlets 134 a,134 b, 134 c and 134 d. In most cases, the telephone jack is part of afaceplate which is secured to an in-wall structure via screws 136 aa and136 ab, corresponding screws not shown in the figure being applicable toall other outlets. Telephone wiring segment 133 a connects the externallocal-loop (typically via an external connection box) to the outlet 134a. Telephone wiring 133 b connects outlets 134 a and 134 b, and as suchRJ-11 jack is actually a connection point for wiring segments 133 a and133 b. Similarly, wiring segment 133 c connects outlets 134 b and 134 c,and wiring segment 133 d connects outlets 134 b and 134 d. Thus, outlet134 b serves as a connection point for the three segments 133 b, 133 cand 133 d.

In many cases it is beneficial to explore the wiring topology in thehouse. For example, in the case wherein the telephone wiring is used fordata communication (such as HomePNA mentioned above), knowing thetopology enables installing proper terminations to the wires, hencereducing reflections and improving the communication characteristics.However, since the telephone wires are hidden in the walls of the house,there is no simple and direct way to know the wiring topology in thebuilding. Dismantling the outlets from the walls to investigate thehidden wiring topology is cumbersome, time-consuming, expensive and willmost likely require a professional worker (e.g. electrician, telephonetechnician). Using the CIM offers an easy and quick way of investigatingthe topology, using the pairs count method described above. For example,it is assumed that the telephone wire-pair characteristic impedance (inthe bandwidth measured) is about 120 ohms. Connecting the CIM to outlet134 a (direct connection to RJ-11 jack 135 a) will result in a measuredimpedance of 120/2=60 ohms, since the two wiring segments 133 a and 133b are connected thereto. Similarly, connecting to jack 135 b of outlet134 b will measure 120/3=40 ohms, due to the three connected segments133 b, 133 d, and 133 c. Similarly, outlets 134 d and 134 c will resultin 120 ohms, since a single segment is connected thereto (120/1=120).Thus, the CIM can provide the data about the number of wiring segmentsconnected to a specific outlet. In the above example, a set ofmeasurements in all the house outlets will clearly indicate that onlyoutlets 134 d and 134 c are connected to a single wiring segment, and assuch are the only ones requiring termination.

In addition to topology finding, the CIM may also be used to measure theactual characteristic impedance of any hidden wiring segments, such asthe in-wall telephone-wiring infrastructure 130. By connecting forexample to the connector 135 c of outlet 134 c (known to be connected toa single wiring segment), the CIM can be used to measure thecharacteristic impedance of the wiring segment 133 c connected thereto,thus allowing for adapting a proper termination value.

While the invention has been described with regard to telephone wiring,it will be appreciated that the same problem and benefits applies toelectrical wiring within a building, used for distributing AC power inthe house (115 VAC 60 Hz in North America and 220 VAC/50 Hz in Europe,for example). An example of such existing telephone wiring structure isshown in FIG. 14 as system 140, involving AC power wiring infrastructurewithin the walls of a building 132. The in-house AC power wiringconnects to the external power distribution system 141 (typically viathe nearest transformer) via a single (or more) AC power wire pair(typically third conductor is ground or earth potential) connected to ajunction box 147 a, serving as a ‘demarcation-point’. The AC powerwiring is accessed in the house via AC power outlets 144 a, 144 b, 144 cand 144 d. Each such outlet 144 connects to the in wall wiring, andallows for connection thereto via a front connector 145, commonly areceptacle/jack having two or three female connectors, suitable forconnection of an appliance via respective prongs a suitable AC powerplug. As shown for system 140, AC power jacks 145 a, 145 b, 145 c and145 d are respectively part of outlets 144 a, 144 b, 144 c and 144 d. Inmost cases, the AC power receptacle is part of a faceplate which issecured to an in-wall structure via screws 146 aa and 146 ab,corresponding screws not shown in the figure being applicable to allother outlets as well. Unlike the telephone wiring structure shown assystem 130 above, AC power wiring commonly uses junction boxes formultiple AC power wiring segment connections, such as junction box 147b. AC Power wiring segment 143 a connects the junction box 147 a to theoutlet 144 a. AC power wiring 143 b connects outlet 144 a and junctionbox 147 b. Similarly, wiring segments 143 c and 143 e respectivelyconnect outlets 144 c and 144 b to junction box 147 b, and wiringsegment 143 d connects outlet 144 d to junction box 147 a. Thus, outlet144 a serves as a connection point for the two segments 143 a and 143 b.In a similar way to the above data communication over telephone wiring,such AC power wiring may be used for data communication concurrentlywith the AC power distribution functionality (e.g. using HomePlugstandard). In such a system, the CIM can be used (by connecting to therelevant AC connector 145 of a tested outlet 144) to determine which ACpower outlets are located at the end of a wire such as outlets 144 b,144 c and 144 d (and should be thus well terminated) and which outlets(such as outlet 144 a) should not be terminated since it is not acommunication end point. In addition, the CIM may be used to measure thecharacteristic impedance of an AC power segment thus enabling theinstallation of a proper termination wherever required.

While the invention has been demonstrated with regard to telephone andAC power wiring, it will be appreciated that the invention can equallybe applied to any hidden wiring such as in-wall residential wiring, andspecifically to CATV wiring. CATV wiring is used to distribute CATV anddata signals throughout the house, and is based on coaxial-cable mediumand CATV outlets having RF connectors such as BNC and F-Type. Likewise,the invention will find application where wiring is partially hiddenand/or where it is routed in such manner (for example via severalmutually adjacent rooms or floors) such that even if the wiring isvisible, its topology is not readily discernible. Thus, the term“in-wall” when used in the description and appended claims encompassesalso such applications.

In the above in-wall wiring applications for service wiring, comprisingCATV, AC power or telephone wiring, the method 70 step 72 comprisesconnecting to the in-wall wiring, typically via the telephone connector135 of the telephone outlet 134 in the telephone wiring application, orvia the AC power connector 145 in the AC power outlet 144 in the ACpower application, or via the RF connector that is part of a CATVoutlet. Similarly, operation 77 involving CIM disconnecting comprisesdisconnecting from the connector in the outlet.

Housing/Packaging

The CIM 30 described above, with or without the termination settingmechanism shown a system 40, as well as system 80 b, may be housedand/or integrated within an enclosure (in part of in full) as warrantedby the application. In some embodiments, the CIM will be housed as adistinct, separately packaged and stand-alone device. Such an exemplarydevice 150 used as a handheld test-set device for testing the number ofconnected wiring segments and the characteristic impedance of atelephone wiring system in a residential house, as described aboveregarding wiring system 130, is shown in FIG. 15. The device 150connects to the telephone outlet 134 RJ-11 jack connector 135 by a RJ-11plug 151, and upon operation shows the measured characteristic impedancein ohms in the numeric display 153. Similarly, a pairs count may bemeasured as per the above described method, and the count of the pairsis displayed by light in the appropriate visual indicators (such asLEDs), wherein indicators 152 a, 152 b, 152 c and 152 d respectivelyrepresent 1, 2, 3 and 4 pairs counting.

In other embodiments, the CIM 30 (with or without a termination settingsuch as system 40), as well as system 80 b, is not separated but ratherintegrated with the modem or transceiver used for data communicationover the wiring or the transmission-line. In such a case, the housingcomprising the modem will be also used to house the CIM and its relatedand associated components.

Similar to the above discussion regarding housing of modems operative tocarry data over active service wiring (to include telephone, AC powerand CATV), the CIM related circuitry may be embedded (in part or infull) in an outlet (with or without a respective modem) or in a modulemechanically and electrically attachable/detachable to a service outlet(to include telephone, AC power and CATV outlets). An example of such anoutlet snap-on module for use with AC power outlet in North America isshown as module 160 in FIG. 16. The module 160 is mechanicallyattachable and electrically connectable to an AC power outlet 144 (asshown in FIG. 14) by two power prongs 161 a and 161 b, to be insertedinto the respective female connectors of the AC power jack 145. Module160 is shown to comprise a powerline modem (such as HomePlug basedmodem) allowing data units connected via IEEE802.3 10/100BaseT RJ-45jack 162 to communicate over the AC power medium. Such module 160typically comprises one or more visual indicators such as 163 a shown,in order to report the system status to the user.

Operation Modes.

Various operating timing modes may be used involving characteristicimpedance measuring.

Continuous mode: In such embodiment the characteristic impedance iscontinuously measured. Such operation is obtained by activating the‘Delay’ 69 in the operational sequence 70. As such, upon completing ameasurement sequence, the sequence re-starts from operation 72 oroperation 74, causing another pulse to be transmitted and measured. Inthe case wherein no reflections are expected (e.g. long transmissionline or well terminated line), the delay may be a minimum or even zero.In the case wherein reflections may occur, the delay should becalculated such that no reflections will be sensed upon the measuringoperation 75. Similarly, continuous operation may use periodicoperation, wherein the system is activated at fixed (or variable)intervals, based on the delay incurred in operation 69. In the casewherein the transmission line is also used for data communication, careshould be taken that the pulse transmitted for the characteristicimpedance measurement will not interfere with the data communicationsystem operation. If the system is used solely for measurement (e.g. astest set) such as for pairs counting, such precautions are not required.It should be noted that measuring/setting termination value system 80 bcan also work continuously (or periodically), without affecting the datacommunication operation.

In continuous mode of operation, setting of termination value may alsobe continuous, wherein the set value tracks the continuous or periodicmeasured characteristic impedance, or alternatively may be set uponmeasuring a more than threshold change, or upon external controlcommand.

One-time operation mode: In such embodiment the operational sequence 70shown in FIG. 7 is operated once, and resumes its non-operational stateafter sequence completion. In such mode, the need for operation 69 isobviated. The ‘start’ operation 71 initializing the process may beoperated automatically or upon external control (outside the CIM unit)request. In one embodiment, initialization of the measurement isinitiated upon powering up the unit. In another embodiment, the modemmay initiate measuring (and setting of the termination value) at everycommunication session initialization. In yet another embodiment, thesystem will commence operation upon manual request (e.g. button push) bya user. Similarly applying for system 80 b, the loop operation will beallowed only once for a short period, and the set value will be lockedafterwards.

Packet-based operation: While the invention has been demonstrated withregard to CIM 30 generating a specific dedicated pulse only for thepurpose of the characteristic impedance measurement, it will beappreciated that the invention can equally be applied to the casewherein the energy used for the measurement is part of a modem regulardata communication operation. Particularly, in packet- or burst-basedcommunication, wherein a transmitter is not continuously transmittingbut rather intermittently, the packet transmitted can serve also for thepurpose of measuring the characteristic impedance. Typically packetsused in the art, such as IEEE802.3, comprise four parts (commonlyreferred to as fields), illustrated as packet 170 as shown in FIG. 17.The first transmitted part is a preamble 171, used for synchronizationand receiver training, followed by a header field 172 comprisingoverhead and management information such as an address. The actual data173 is next transmitted, followed by a trailer field 174 (comprisingchecksum, for example). Soon after the packet start, the measurement canbe executed, based on the energy transmitted as part of the preamble,for example, as shown in timing line 175. In such a configuration, ameasurement may be performed based on the packets timing. For example,operation may be initiated upon each packet sent or every multiplepacket set.

Setting of termination value, if required, may also be continuous,one-time or packet-based. In each case, the set value may track thecontinuous, periodic or one-time measured characteristic impedance, oralternatively may be set upon measuring a more than threshold change, orupon external control command.

An example of implementation guidelines is shown as system 180 in FIG.18. A CIM 30 is shown, wherein operation is initiated by coupling apulse to input 31 (‘Measure’). A pulse generator 184, such as based onthe 555 family of integrated circuit timers known in the art, may beconnected to the ‘measure’ port 31, repetitively and periodicallysending pulses to the CIM 30, implementing a continuous and/or periodicmode of operation. Alternatively, there is provided a power-up circuitcomprising a resistor 181, a capacitor 182 and an inverting gate 185(preferably having Schmitt-trigger function) such as 74HC14. Beforepower-up, capacitor 182 is discharged. Upon powering the circuit,capacitor 182 is charged, causing the gate 185 output to generate ashort ‘Measure’ pulse, thus initiating a onetime operation upon eachsystem powering-up. Furthermore, manual initiation may be added byconnecting a switch button 183 in parallel to the capacitor 182. Uponswitch 183 contacts closing, the capacitor is discharged and a ‘Measure’pulse is regenerated.

While the invention has been demonstrated with various operation modessuch as continuous, periodic, manually, one-time and per-packetoperations, it will be appreciated that the invention can equally beapplied to any combination of the above modes. For example, a system maybe initiated upon power-on and then periodically or communicationsession-timed. Furthermore, the system may shift from mode to modeduring operation upon external control.

For many applications involving digital data communication, thecharacteristic impedance of a line may be practically regarded as havinga pure resistance. While the invention has been demonstrated aboverelating to a pure-resistance based termination, it will be appreciatedthat the invention can equally be applied to any type of termination,including a termination comprising a complex impedance, using theembodiment of FIG. 5, for example. Furthermore, both linear andnon-linear terminations may be considered. Furthermore, while theinvention has been demonstrated above relating to matching a terminationvalue to the characteristic impedance of a line in order to reducereflections, it will be appreciated that the invention can equally beapplied to any application wherein a matching termination is notdeployed. In these applications, the measured characteristic impedancevalue may be used as a basis to the termination value to install, thusenabling the control of the mismatch and the level of generatedreflections, instead of trying to eliminate them altogether. Forexample, slight mis-match may be used in digital data transmission inorder to improve the rise/fall time of the signal.

While the invention has been demonstrated above relating to a paralleltermination wherein the termination device is directly connected to thetwo conductors comprising the wired transmission-line, it will beappreciated that the invention can equally be applied to any type oftermination arrangement or topology, such as serial (a.k.aback-matching), power and bi-directional, as described in NationalSemiconductor Corporation Application Note 903 (August 1993) entitled:“A Comparison of Differential Termination Techniques”. Furthermore, theinvention can be applied in both balanced and unbalanced lines, as wellas in both lossy and lossless lines.

While the invention has been demonstrated above relating to a digitaldata communication comprising electrical signals propagating over wiredtransmission-line, it will be appreciated that the invention can equallybe applied to any type of electrical signal, including analog signals.

While the invention has been described with regard to a metallictransmission-line comprising two conductors and carrying electricalsignals, it will be appreciated that the invention can equally beapplied to any type of transmission-line, including any electric wavetransmission systems wherein electromagnetic wave energy is guided orconstrained by a wave transmission guide. Such wave transmission linesinclude passive or active wave transmission networks simulating thecharacteristics of a long line wave transmission systems or wave guides,such as artificial lines, delay networks, resonators, impedance matchingnetworks, equalizers, loaded lines and wave filters.

While the invention has been described with regard to a terminationconsisting of a single passive element (e.g. resistor), it will beappreciated that the invention can equally be applied to any type oftermination arrangement, including passive or active elements, includingimpedance matching networks, hybrid networks, coupling networks, waveshaping networks, phase shifting networks, wave filters, equalizers andattenuators. Active elements include devices for producing across atleast two of the system terminals a negative resistance, and/or aninductance, or capacitance, wherein each of the above may be positive ornegative.

Public Notice Regarding the Scope of the Invention and Claims

While the invention has been described in terms of preferred embodimentsand generally associated methods, the inventor contemplates thatalterations and permutations of the preferred embodiments and methodswill become apparent to those skilled in the art upon a reading of thespecification and a study of the drawings.

Accordingly, neither the above description of preferred exemplaryembodiments nor the abstract defines or constrains the invention.Rather, the issued claims variously define the invention. Each variationof the invention is limited only by the recited limitations of itsrespective claim, and equivalents thereof, without limitation by otherterms not present in the claim. In addition, aspects of the inventionare particularly pointed out in the claims using terminology that theinventor regards as having its broadest reasonable interpretation; morespecific interpretations of 35 U.S.C. section. 112 (6) are only intendedin those instances where the term “means” is actually recited. The words“comprising,” “including,” and “having” are intended as open-endedterminology, with the same meaning as if the phrase “at least” wereappended after each instance thereof.

1. A method for estimating the number of wire pairs connected to asingle connection point, where all wire pairs have a similar nominalcharacteristic impedance Z0, the method comprising: connecting acharacteristic impedance measuring device to the connection point;measuring the lumped impedance Z presented by the wire pairs at theconnection point; and calculating Z0/Z to provide an estimate of thenumber of wire pairs connected to the connection point.
 2. The methodaccording to claim 1, further comprising storing the measured impedancevalue or a representation of the estimate of the number of wire pairs.3. The method according to claim 1, further comprising providing avisual indication of the measured impedance value or the estimate of thenumber of wire pairs.
 4. The method according to claim 1, wherein thewire pairs are at least partially hidden in the wall of a building, theconnection point is an outlet having a front faceplate, and connectingto the connection point comprises connecting to a connector on the frontfaceplate of the outlet.
 5. The method according to claim 4, wherein thewire pairs form part of a telephone, AC power, or CATV wiringinfrastructure, and the outlet is a telephone, AC power, or CATV outlet,respectively.
 6. The method according to claim 5, wherein theinfrastructure carries a signal in a first frequency band, and measuringthe lumped impedance comprises transmitting energy to the connectionpoint in a second frequency band distinct from the first frequency band.7. The method according to claim 1, further comprising: identifying awiring end-point having a single connection wherein the connection pointlumped impedance is Z0, and connecting a termination to the connectionpoint of the identified wiring end-point.
 8. The method according toclaim 1, wherein the wire pairs are at least partially hidden in thewall of a building, the connection point is an outlet, and connecting acharacteristic impedance measuring device to the connection pointcomprises integrating the measuring device into the outlet.
 9. Themethod according to claim 1, wherein a modem for communication isconnected to the connection point, and said method further comprises apreliminary operation of disconnecting the modem from the connectionpoint, and a subsequent operation of re-connecting the modem to theconnection point.
 10. The method according to claim 1, wherein measuringand calculating are initiated periodically, or upon application of anexternal signal, or upon a manual action, or upon powering up of themeasuring device.
 11. A device for estimating the number of wire pairsconnected to a single connection point, where one or more wire pairshaving a similar nominal characteristic impedance Z0 are all connectedto the single connection point, said device comprising: a port forconnecting to the connection point, a lumped impedance measuring unitcoupled to said port for instantaneously measuring the connection pointlumped impedance Z, and a Z0/Z calculator coupled to the lump impedancemeasuring unit for estimating the connected wire pairs count to be Z0/Z.12. The device according to claim 11, further comprising a memorycoupled to said lump impedance measuring unit for storing the measuredlumped impedance value or a representation of calculated number ofwire-pairs.
 13. The device according to claim 11, further comprising avisual indicator for displaying the measured lumped impedance value orthe calculated number of wire-pairs.
 14. The device according to claim11, for use when the wire pairs are at least partially hidden in a wallof a building, the connection point is an outlet having a frontfaceplate, wherein said port comprises a connector that mates to acomplementary connector on the front faceplate of the outlet.
 15. Thedevice according to claim 14, wherein the wire pairs form part of atelephone, AC power, or CATV wiring infrastructure, the outlet is atelephone, AC power, or CATV outlet, respectively, and said connector isa telephone, AC power, or CATV plug, respectively.
 16. The deviceaccording to claim 15, wherein the infrastructure carries a signal in afirst frequency band, and said lump impedance measuring unit comprises:an energy transmitter coupled to said connector for transmitting energyto the connection-point said energy being carried in a second frequencyband distinct from the first frequency band.
 17. The device according toclaim 11, further comprising: means for identifying a wiring end-pointhaving a single connection wherein the connection point lumped impedanceis Z0, and means for connecting a termination to the connection-point ofan identified wiring end-point.
 18. The device according to claim 11 foruse when the wire pairs are at least partially hidden in the wall of abuilding, wherein the connection point is an outlet, and said device isat least in part integrated into the outlet.
 19. The device according toclaim 11 for use with a modem for communication over the wire pairs,wherein the device further comprises a selective connection unit fordisconnecting the modem from the connection point and for re-connectingthe modem to the connection point.
 20. The device according to claim 11,further comprising a selector for operating said device eitherperiodically, or upon application of an external signal, or upon amanual action, or upon powering up of the device.
 21. A method formatching a termination to a wired transmission-line using aclosed-control loop, the transmission-line being connected to carry asignal and having a nominal characteristic impedance, the methodcomprising: connecting a termination having a controllable impedancevalue to the transmission-line; measuring the power dissipated bytermination; and changing the termination impedance value to obtain amaximum power dissipation by the termination.
 22. The method accordingto claim 21, further comprising storing a representation of thetermination value.
 23. The method according to claim 21, wherein saidmeasuring comprises directly measuring at least one of the voltageacross the termination and the current through the termination.
 24. Themethod according to claim 21, wherein said measuring comprisesindirectly measuring the dissipated power by measuring a physicalphenomena affected by the dissipated power.
 25. A device for matching atermination to a wired transmission line using a closed-control loop,the transmission-line being connected to carry a signal and having anominal characteristic impedance, said device comprising: a port forconnecting to the wired transmission line, a termination having avariable impedance value coupled to said port and having a control port,means for measuring power dissipated coupled to said termination, andcontrol means coupled between said means for measuring and said controlport for closed loop control operative for changing the impedance valueof said termination to maximize power dissipated in said terminationwhen power is supplied to the transmission line.
 26. The deviceaccording to claim 25, further comprising a memory for storing arepresentation of the termination impedance value.
 27. The deviceaccording to claim 25, wherein power dissipated in said termination isdirectly measured by measuring at least one of the voltages across saidtermination and the current through said termination.
 28. The deviceaccording to claim 25, wherein power dissipated in said termination isindirectly measured by measuring a physical phenomena affected by thedissipated power.
 29. A method for estimating an optimum impedance valuefor a termination to a wired transmission line having a lumped impedanceZ comprising: connecting a characteristic impedance measuring device tothe wired transmission line, instantaneously measuring the lumpedimpedance Z, and estimating an optimum termination value based on themeasured value Z.
 30. The method according to claim 29, furthercomprising storing a representation of the measured lumped impedancevalue.
 31. The method according to claim 29, wherein the estimated valueis equal to the measured value Z.
 32. The method according to claim 29,further comprising connecting a termination having the estimated valueto the wired transmission line.
 33. The method according to claim 29,wherein the wired transmission line comprises a wire pair at leastpartially hidden in the wall of a building and connected to an outlethaving a front faceplate, and said connecting a characteristic impedancemeasuring device to the wired transmission line comprises connecting thedevice to a connector on the front faceplate of the outlet.
 34. Themethod according to claim 33, wherein the wire pair is part of atelephone, AC power, or CATV wiring infrastructure, and said outlet is atelephone, AC power, or CATV outlet, respectively.
 35. The methodaccording to claim 34, wherein the infrastructure carries a signal in afirst frequency band and said step of measuring comprises transmittingenergy to the transmission line, the energy being in a second frequencyband distinct from the first frequency band.
 36. The method according toclaim 29, wherein the wired transmission line comprises wire pairs atleast partially hidden in the wall of a building, at least one of thewire pairs is connected to an outlet, and said method comprises thepreliminary operation of integrating the measuring device into theoutlet.
 37. The method according to claim 29 for use with a modem forcommunication over the wired transmission line, wherein the wiredtransmission line comprises wire pairs, and said method furthercomprises: initiating said measuring operation by disconnecting themodem from the wired transmission line; and re-connecting the modem tothe transmission-line after said measuring operation.
 38. The methodaccording to claim 29, wherein said measuring and estimating operationsare initiated periodically, or upon application of an external signal,or upon a manual action, or upon powering up of the measuring device.39. A device for estimating the termination to a wiredtransmission-line, the device comprising: a port for connecting to thewired transmission-line, impedance measuring unit coupled to said portfor instantaneously measuring the lumped impedance Z of thetransmission-line, and means coupled to said impedance measuring unitfor estimating the optimal termination value of the transmission-linebased on the measured value Z.
 40. The device according to claim 39,further comprising a memory coupled for storing the measured lumpedimpedance value.
 41. The device according to claim 39, wherein theestimated value is equal to the measured value Z.
 42. The deviceaccording to claim 39, further comprising means for connecting atermination having the estimated value to the wired transmission-line.43. The device according to claim 39, wherein the wiredtransmission-line comprises a wire pair at least partially hidden in thewall of a building and connected to an outlet having a front faceplate,and said port comprises a connector for connecting to a furtherconnector on the front faceplate of the outlet.
 44. The device accordingto claim 43, wherein the wire pair is part of a telephone, AC power, orCATV wiring infrastructure, and the outlet is a telephone, AC power, orCATV outlet, respectively.
 45. The device according to claim 44, whereinthe infrastructure carries a signal in a first frequency band, and saidimpedance measuring unit comprises: an energy transmitter coupled tosaid connector for transmitting energy to the wired transmission-line;the energy being carried in a second frequency band distinct from thefirst frequency band.
 46. The device according to claim 39, beingintegrated into an outlet.
 47. The device according to claim 39, for usewith a modem for communication over the wired transmission-line, whereinsaid device further comprises a switch for disconnecting the modem fromthe wired transmission-line, and for re-connecting the modem to thetransmission-line.
 48. The device according to claim 39, furthercomprising a selector for operating said device either periodically, orupon application of an external signal, or upon a manual action, or uponpowering up of the device.